Unraveling the light-promoted synergy between highly dispersed Ni and Ni nanoparticles for efficient photothermocatalytic cellulose steam reforming to syngas†

As a sustainable strategy for renewable biomass conversion to green syngas (H₂ and CO), photothermocatalytic cellulose steam reforming encounters arduous challenges, including high byproduct selectivities, low efficiency, and susceptibility to deactivation. Herein, we report a photothermocatalyst (10Ni/MgO_ET) with suitable dual-site composition of highly dispersed Ni and Ni nanoparticles (NPs) for the breakdown of complex byproducts. It achieved an optimized photothermocatalytic production rate of syngas (r_H2 of 4986.6 mmol g_catalyst⁻¹ h⁻¹, r_CO of 2752.7 mmol g_catalyst⁻¹ h⁻¹) and light-to-fuel efficiency (8.3%) among the photocatalysts and photothermocatalysts reported so far. Characterization results revealed that the enhanced photothermocatalytic activity is due to a remarkable synergy in H₂O dissociation to O* by highly dispersed Ni sites and tar cracking by Ni NPs. In particular, photoactivation promotes the synergy by accelerating H₂O dissociation to O* (with release of H₂) and O* activation, thus enhancing the conversion of tar to syngas and preventing the deactivation caused by char encapsulation. Thus, these findings offer an excellent strategy and insightful mechanistic understanding of photothermocatalytic syngas production.